There is a growing demand for multicasting video over wireless links due to the recent surge in the number of mobile devices such as laptops, handheld PDAs and cellular phones. The wireless channel however introduces severe impairments at the physical layer which in turn translates into severe packet losses and longer delays at the application layer, making a smooth delivery of video highly challenging. Furthermore, bandwidth comes for a huge premium in wireless systems. Accordingly, a common channel is typically shared across users intending to download the same media stream. However, the physical link characteristics of different users sharing the same wireless link are in general different and highly sensitive to their location, mobility and other aspects.
A common approach for dealing with erasures at the application layer is retransmission. The sender has a sequence of packets to send to the receiver and it continues transmitting the same packet until it is received successfully by the receiver (i.e., it receives an acknowledgement) or a timeout occurs. While retransmissions are quite effective in a point-to-point scenario, they do not scale with the number of users in a point-to-multipoint scenario.